Audio Fact(s) of the Day

I just wanted to post some random facts about sound and how we perceive it. I encourage you to follow the links and find out more. Well, here you go:

loudness is not directly proportional to the pressure that sound wave applies to your ear;

sounds of the same pressure but different tones would appear to have different loudness. Humans are most sensitive to frequencies from about 2 kHz to 5 kHz. A-weighting curve (along with a bunch of others) describe the connection;

there’s no single unit to measure loudness. We have dBSPL, decibel using 20 micropascals as a reference value. There’s dB(A), which is just dBSPL corrected in accordance with A-weighting curve. There’s also phon, defined as an equal to 1 dBSPL at a frequency of 1 kHz, and then scaled for other frequencies, forming equal-loudness contour;

in digital systems it’s all backwards: 0 dBFS (“decibel relative to full scale”) is the loudest sound possible, and anything else is encoded by negative values (e.g., -3 dBFS is half as loud as possible);

specifics of human hearing can be described with psychoacoustic model. It is then used in “lossy” codecs (MP3, Ogg Vorbis, etc.) to exclude sounds that you are unlikely to hear, thus allowing for better compression;